Automated digestion and extraction apparatus for use in the determination of trace metals in foodstuffs

Abstract

An automated system has been constructed that uses a displacement technique to transfer foodstuffs, previously converted into a fluid state, into a modified Technicon digestor where a wet oxidation is carried out at 400 °C with the aid of sulphuric acid, nitric acid and hydrogen peroxide. The digest is pumped into a neutralisation unit where its pH is adjusted to a pre-set value and then flows into an extraction unit where the metals of interest are chelated and extracted into an immiscible organic solvent. Finally, the organic phase is separated and collected for subsequent analysis by plasma-emission spectrometry. The operation of the system is fully automatic and it processes 5–8-g samples at the rate of three per hour. Results obtained with the automatic system for the determination of iron, copper and zinc in a wide range of foodstuffs compare favourably with those obtained by manual techniques. Some preliminary results for the determination of cadmium, cobalt, nickel and lead are presented.